Constant fold more unary and binary expressions (#15202)

Now mypy can constant fold these additional operations:

- Float arithmetic
- Mixed int and float arithmetic
- String multiplication
- Complex plus or minus a literal real (eg. 1+j2)

While this can be useful with literal types, the main goal is to improve
constant folding in mypyc (mypyc/mypyc#772).

mypyc can also fold bytes addition and multiplication, but mypy cannot
as byte values can't be easily stored anywhere.

mypy/constant_fold.py

@@ -8,11 +8,21 @@
 from typing import Union
 from typing_extensions import Final
 
-from mypy.nodes import Expression, FloatExpr, IntExpr, NameExpr, OpExpr, StrExpr, UnaryExpr, Var
+from mypy.nodes import (
+    ComplexExpr,
+    Expression,
+    FloatExpr,
+    IntExpr,
+    NameExpr,
+    OpExpr,
+    StrExpr,
+    UnaryExpr,
+    Var,
+)
 
 # All possible result types of constant folding
-ConstantValue = Union[int, bool, float, str]
-CONST_TYPES: Final = (int, bool, float, str)
+ConstantValue = Union[int, bool, float, complex, str]
+CONST_TYPES: Final = (int, bool, float, complex, str)
 
 
 def constant_fold_expr(expr: Expression, cur_mod_id: str) -> ConstantValue | None:
@@ -39,6 +49,8 @@ def constant_fold_expr(expr: Expression, cur_mod_id: str) -> ConstantValue | Non
         return expr.value
     if isinstance(expr, FloatExpr):
         return expr.value
+    if isinstance(expr, ComplexExpr):
+        return expr.value
     elif isinstance(expr, NameExpr):
         if expr.name == "True":
             return True
@@ -56,26 +68,60 @@ def constant_fold_expr(expr: Expression, cur_mod_id: str) -> ConstantValue | Non
     elif isinstance(expr, OpExpr):
         left = constant_fold_expr(expr.left, cur_mod_id)
         right = constant_fold_expr(expr.right, cur_mod_id)
-        if isinstance(left, int) and isinstance(right, int):
-            return constant_fold_binary_int_op(expr.op, left, right)
-        elif isinstance(left, str) and isinstance(right, str):
-            return constant_fold_binary_str_op(expr.op, left, right)
+        if left is not None and right is not None:
+            return constant_fold_binary_op(expr.op, left, right)
     elif isinstance(expr, UnaryExpr):
         value = constant_fold_expr(expr.expr, cur_mod_id)
-        if isinstance(value, int):
-            return constant_fold_unary_int_op(expr.op, value)
-        if isinstance(value, float):
-            return constant_fold_unary_float_op(expr.op, value)
+        if value is not None:
+            return constant_fold_unary_op(expr.op, value)
     return None
 
 
-def constant_fold_binary_int_op(op: str, left: int, right: int) -> int | None:
+def constant_fold_binary_op(
+    op: str, left: ConstantValue, right: ConstantValue
+) -> ConstantValue | None:
+    if isinstance(left, int) and isinstance(right, int):
+        return constant_fold_binary_int_op(op, left, right)
+
+    # Float and mixed int/float arithmetic.
+    if isinstance(left, float) and isinstance(right, float):
+        return constant_fold_binary_float_op(op, left, right)
+    elif isinstance(left, float) and isinstance(right, int):
+        return constant_fold_binary_float_op(op, left, right)
+    elif isinstance(left, int) and isinstance(right, float):
+        return constant_fold_binary_float_op(op, left, right)
+
+    # String concatenation and multiplication.
+    if op == "+" and isinstance(left, str) and isinstance(right, str):
+        return left + right
+    elif op == "*" and isinstance(left, str) and isinstance(right, int):
+        return left * right
+    elif op == "*" and isinstance(left, int) and isinstance(right, str):
+        return left * right
+
+    # Complex construction.
+    if op == "+" and isinstance(left, (int, float)) and isinstance(right, complex):
+        return left + right
+    elif op == "+" and isinstance(left, complex) and isinstance(right, (int, float)):
+        return left + right
+    elif op == "-" and isinstance(left, (int, float)) and isinstance(right, complex):
+        return left - right
+    elif op == "-" and isinstance(left, complex) and isinstance(right, (int, float)):
+        return left - right
+
+    return None
+
+
+def constant_fold_binary_int_op(op: str, left: int, right: int) -> int | float | None:
     if op == "+":
         return left + right
     if op == "-":
         return left - right
     elif op == "*":
         return left * right
+    elif op == "/":
+        if right != 0:
+            return left / right
     elif op == "//":
         if right != 0:
             return left // right
@@ -102,25 +148,41 @@ def constant_fold_binary_int_op(op: str, left: int, right: int) -> int | None:
     return None
 
 
-def constant_fold_unary_int_op(op: str, value: int) -> int | None:
-    if op == "-":
-        return -value
-    elif op == "~":
-        return ~value
-    elif op == "+":
-        return value
+def constant_fold_binary_float_op(op: str, left: int | float, right: int | float) -> float | None:
+    assert not (isinstance(left, int) and isinstance(right, int)), (op, left, right)
+    if op == "+":
+        return left + right
+    elif op == "-":
+        return left - right
+    elif op == "*":
+        return left * right
+    elif op == "/":
+        if right != 0:
+            return left / right
+    elif op == "//":
+        if right != 0:
+            return left // right
+    elif op == "%":
+        if right != 0:
+            return left % right
+    elif op == "**":
+        if (left < 0 and isinstance(right, int)) or left > 0:
+            try:
+                ret = left**right
+            except OverflowError:
+                return None
+            else:
+                assert isinstance(ret, float), ret
+                return ret
+
     return None
 
 
-def constant_fold_unary_float_op(op: str, value: float) -> float | None:
-    if op == "-":
+def constant_fold_unary_op(op: str, value: ConstantValue) -> int | float | None:
+    if op == "-" and isinstance(value, (int, float)):
         return -value
-    elif op == "+":
+    elif op == "~" and isinstance(value, int):
+        return ~value
+    elif op == "+" and isinstance(value, (int, float)):
         return value
     return None
-
-
-def constant_fold_binary_str_op(op: str, left: str, right: str) -> str | None:
-    if op == "+":
-        return left + right
-    return None

mypy/nodes.py

@@ -1002,7 +1002,7 @@ def __init__(self, name: str, type: mypy.types.Type | None = None) -> None:
         # If constant value is a simple literal,
         # store the literal value (unboxed) for the benefit of
         # tools like mypyc.
-        self.final_value: int | float | bool | str | None = None
+        self.final_value: int | float | complex | bool | str | None = None
         # Where the value was set (only for class attributes)
         self.final_unset_in_class = False
         self.final_set_in_init = False

mypy/semanal.py

@@ -3394,7 +3394,7 @@ def analyze_simple_literal_type(self, rvalue: Expression, is_final: bool) -> Typ
             return None
 
         value = constant_fold_expr(rvalue, self.cur_mod_id)
-        if value is None:
+        if value is None or isinstance(value, complex):
             return None
 
         if isinstance(value, bool):

mypyc/irbuild/builder.py

@@ -535,25 +535,25 @@ def load_final_static(
             error_msg=f'value for final name "{error_name}" was not set',
         )
 
-    def load_final_literal_value(self, val: int | str | bytes | float | bool, line: int) -> Value:
-        """Load value of a final name or class-level attribute."""
+    def load_literal_value(self, val: int | str | bytes | float | complex | bool) -> Value:
+        """Load value of a final name, class-level attribute, or constant folded expression."""
         if isinstance(val, bool):
             if val:
                 return self.true()
             else:
                 return self.false()
         elif isinstance(val, int):
-            # TODO: take care of negative integer initializers
-            # (probably easier to fix this in mypy itself).
             return self.builder.load_int(val)
         elif isinstance(val, float):
             return self.builder.load_float(val)
         elif isinstance(val, str):
             return self.builder.load_str(val)
         elif isinstance(val, bytes):
             return self.builder.load_bytes(val)
+        elif isinstance(val, complex):
+            return self.builder.load_complex(val)
         else:
-            assert False, "Unsupported final literal value"
+            assert False, "Unsupported literal value"
 
     def get_assignment_target(
         self, lvalue: Lvalue, line: int = -1, *, for_read: bool = False
@@ -1013,7 +1013,7 @@ def emit_load_final(
             line: line number where loading occurs
         """
         if final_var.final_value is not None:  # this is safe even for non-native names
-            return self.load_final_literal_value(final_var.final_value, line)
+            return self.load_literal_value(final_var.final_value)
         elif native:
             return self.load_final_static(fullname, self.mapper.type_to_rtype(typ), line, name)
         else:

mypyc/irbuild/callable_class.py

@@ -17,7 +17,7 @@
 
 
 def setup_callable_class(builder: IRBuilder) -> None:
-    """Generate an (incomplete) callable class representing function.
+    """Generate an (incomplete) callable class representing a function.
 
     This can be a nested function or a function within a non-extension
     class.  Also set up the 'self' variable for that class.

mypyc/irbuild/constant_fold.py

@@ -13,13 +13,10 @@
 from typing import Union
 from typing_extensions import Final
 
-from mypy.constant_fold import (
-    constant_fold_binary_int_op,
-    constant_fold_binary_str_op,
-    constant_fold_unary_float_op,
-    constant_fold_unary_int_op,
-)
+from mypy.constant_fold import constant_fold_binary_op, constant_fold_unary_op
 from mypy.nodes import (
+    BytesExpr,
+    ComplexExpr,
     Expression,
     FloatExpr,
     IntExpr,
@@ -31,10 +28,11 @@
     Var,
 )
 from mypyc.irbuild.builder import IRBuilder
+from mypyc.irbuild.util import bytes_from_str
 
 # All possible result types of constant folding
-ConstantValue = Union[int, str, float]
-CONST_TYPES: Final = (int, str, float)
+ConstantValue = Union[int, float, complex, str, bytes]
+CONST_TYPES: Final = (int, float, complex, str, bytes)
 
 
 def constant_fold_expr(builder: IRBuilder, expr: Expression) -> ConstantValue | None:
@@ -44,35 +42,55 @@ def constant_fold_expr(builder: IRBuilder, expr: Expression) -> ConstantValue |
     """
     if isinstance(expr, IntExpr):
         return expr.value
+    if isinstance(expr, FloatExpr):
+        return expr.value
     if isinstance(expr, StrExpr):
         return expr.value
-    if isinstance(expr, FloatExpr):
+    if isinstance(expr, BytesExpr):
+        return bytes_from_str(expr.value)
+    if isinstance(expr, ComplexExpr):
         return expr.value
     elif isinstance(expr, NameExpr):
         node = expr.node
         if isinstance(node, Var) and node.is_final:
-            value = node.final_value
-            if isinstance(value, (CONST_TYPES)):
-                return value
+            final_value = node.final_value
+            if isinstance(final_value, (CONST_TYPES)):
+                return final_value
     elif isinstance(expr, MemberExpr):
         final = builder.get_final_ref(expr)
         if final is not None:
             fn, final_var, native = final
             if final_var.is_final:
-                value = final_var.final_value
-                if isinstance(value, (CONST_TYPES)):
-                    return value
+                final_value = final_var.final_value
+                if isinstance(final_value, (CONST_TYPES)):
+                    return final_value
     elif isinstance(expr, OpExpr):
         left = constant_fold_expr(builder, expr.left)
         right = constant_fold_expr(builder, expr.right)
-        if isinstance(left, int) and isinstance(right, int):
-            return constant_fold_binary_int_op(expr.op, left, right)
-        elif isinstance(left, str) and isinstance(right, str):
-            return constant_fold_binary_str_op(expr.op, left, right)
+        if left is not None and right is not None:
+            return constant_fold_binary_op_extended(expr.op, left, right)
     elif isinstance(expr, UnaryExpr):
         value = constant_fold_expr(builder, expr.expr)
-        if isinstance(value, int):
-            return constant_fold_unary_int_op(expr.op, value)
-        if isinstance(value, float):
-            return constant_fold_unary_float_op(expr.op, value)
+        if value is not None and not isinstance(value, bytes):
+            return constant_fold_unary_op(expr.op, value)
+    return None
+
+
+def constant_fold_binary_op_extended(
+    op: str, left: ConstantValue, right: ConstantValue
+) -> ConstantValue | None:
+    """Like mypy's constant_fold_binary_op(), but includes bytes support.
+
+    mypy cannot use constant folded bytes easily so it's simpler to only support them in mypyc.
+    """
+    if not isinstance(left, bytes) and not isinstance(right, bytes):
+        return constant_fold_binary_op(op, left, right)
+
+    if op == "+" and isinstance(left, bytes) and isinstance(right, bytes):
+        return left + right
+    elif op == "*" and isinstance(left, bytes) and isinstance(right, int):
+        return left * right
+    elif op == "*" and isinstance(left, int) and isinstance(right, bytes):
+        return left * right
+
     return None

mypyc/irbuild/expression.py

@@ -55,7 +55,6 @@
     Assign,
     BasicBlock,
     ComparisonOp,
-    Float,
     Integer,
     LoadAddress,
     LoadLiteral,
@@ -92,7 +91,6 @@
     tokenizer_printf_style,
 )
 from mypyc.irbuild.specialize import apply_function_specialization, apply_method_specialization
-from mypyc.irbuild.util import bytes_from_str
 from mypyc.primitives.bytes_ops import bytes_slice_op
 from mypyc.primitives.dict_ops import dict_get_item_op, dict_new_op, dict_set_item_op
 from mypyc.primitives.generic_ops import iter_op
@@ -575,12 +573,8 @@ def try_constant_fold(builder: IRBuilder, expr: Expression) -> Value | None:
     Return None otherwise.
     """
     value = constant_fold_expr(builder, expr)
-    if isinstance(value, int):
-        return builder.load_int(value)
-    elif isinstance(value, str):
-        return builder.load_str(value)
-    elif isinstance(value, float):
-        return Float(value)
+    if value is not None:
+        return builder.load_literal_value(value)
     return None
 
 
@@ -662,10 +656,6 @@ def set_literal_values(builder: IRBuilder, items: Sequence[Expression]) -> list[
                 values.append(True)
             elif item.fullname == "builtins.False":
                 values.append(False)
-        elif isinstance(item, (BytesExpr, FloatExpr, ComplexExpr)):
-            # constant_fold_expr() doesn't handle these (yet?)
-            v = bytes_from_str(item.value) if isinstance(item, BytesExpr) else item.value
-            values.append(v)
         elif isinstance(item, TupleExpr):
             tuple_values = set_literal_values(builder, item.items)
             if tuple_values is not None:
@@ -685,7 +675,6 @@ def precompute_set_literal(builder: IRBuilder, s: SetExpr) -> Value | None:
     Supported items:
      - Anything supported by irbuild.constant_fold.constant_fold_expr()
      - None, True, and False
-     - Float, byte, and complex literals
      - Tuple literals with only items listed above
     """
     values = set_literal_values(builder, s.items)